Digital clock - any recommendations?

For that unit you'll need a clock that outputs 44.1, 88.2, and 176.4. Try an Antelope LiveClock and upgrade its wall wart to a good LPS.  If you want to go further, the LiveClock may in turn be synchronized to a 10mhz atomic clock like Mutec, Cybershaft, or Stanford Research System.   

The most affordable
https://www.m2techusa.com/collections/frontpage/products/evo-clock-precision-clock-generator
you must buy an highend  BNC cable
 How cost the Esoteric  compare to your Marantz ?
May be with Marantz , the difference will be subtile

This difference may:
1- not be better2- is very DAC dependent.
From an electrical engineering point of view, you want the clock as physically close to the DAC for the best signal and lowest jitter.

I prefer to get a DAC with a great internal clock, Mytek. Anything outside the case is going to be worse just due to the distance involved.


I suggest you audition your DAC and keep an open mind as to which version sounds better.


Best,

E

How much are you willing to spend?

Any excellent DAC will not benefit from an external clock. The good ones, like the Benchmark DAC3 reclock S/PDIF themselves, so the only jitter is internal.

Why buy a $700 reclocker when you can get $700 or cheaper DAC with external jitter reduction?

For instance, the Schiit Modi 2 showed improvement when the Empirical Audio $700 reclocker was added, but pretty much no difference when used with the Topping DX7s ($500 DAC+headphone amp).

Going digital out of your Marantz to say the SMSL SU-8 would give you similar results to using an external reclocker, in that the jitter from both would be well below audible levels.